On Mar 6, 2011, at 1:52 PM, Ashish Kumar wrote:
In the boot package,consider a scalar function to boot.
estimator <- function(x, d) {
+ mean(x[d])
+ }
data <- city$u
b <- boot(data, estimator, R=1000)
b$t0
[1] 64
ci <- boot.ci(b, type=c("bca"), conf=.95)
ci$bca
conf
[1,] 0.95 49.44 991.39 36.78807 110.0254
Now if I want estimators to return a vector,E.g. it's
{c(mean(x[d]), sd(x[d]))}, boot.ci() should give me
a vector of low bounds and high bounds of the 95% confidence
interval. But that does not happen.
It appears to have happened. The last two numbers in the output below
are what are supposed to be your CI.
estimator <- function(x, d) {
+ c(mean(x[d]), sd(x[d]))
+ }
data <- city$u
b <- boot(data, estimator, R=1000)
b$t0
[1] 64.00000 56.21585
So you got a vector of estimates. What is the problem? did you look at
str(b)?
ci <- boot.ci(b, type=c("bca"), conf=.95)
ci$bca
conf
[1,] 0.95 68.27 995.48 39.2 105.4292
You may have mis-informed boot.ci, since it was expecting the second
column to be variances and you supplied it sd's. Look at the
documentation for the index argument in boot.ci.
--
David Winsemius, MD
Heritage Laboratories
West Hartford, CT
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